Snort HTTP Inspect Pre-Processor Uricontent Bypass

2006-06-05 / 2006-06-06
Risk: Medium
Local: No
Remote: Yes
CWE: CWE-264


CVSS Base Score: 5/10
Impact Subscore: 2.9/10
Exploitability Subscore: 10/10
Exploit range: Remote
Attack complexity: Low
Authentication: No required
Confidentiality impact: None
Integrity impact: None
Availability impact: Partial

For those of you using snort on this list, this got posted to some of the snort mailing lists this morning. http://www.demarc.com/support/downloads/patch_20060531 http://www.osvdb.org/25837 "The evasion technique allows an attack to bypass detection of "uricontent" rules by adding a carriage return to the end of a URL, directly before the HTTP protocol declaration. This affects thousands of rules in the standard Snort base rule sets. Due to the seriousness of this vulnerability, we have developed a working patch for public review. See below. This patch addresses the carriage return bug and should catch the known evasion attempts but further research needs to be done to determine if there are any other possible impacts of this bug. The detection for evasion is turned on by default under all profiles but can also be used as a server configuration option: -----HTTP Inspect Server Configuration----- non_std_cr <yes|no> This option generates an alert when a non standard carriage return character is detected in the URI. -----end----- More information including a pre-patched tarball, a simple proof of concept, and a copy of this patch ..." feofil


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